1. Field of the Invention
The present invention relates to hydro-turbine units submerged in rivers, ocean currents and especially those which convert the kinetic energy of the water current into electrical energy. Typically, these units consist of a bulb housing and a rotating system consisting of turbine runner, turbine shaft, turbine shaft seal, bearings, speed increasing transmission, electrical generator and shaft couplings. The additional auxiliary equipment provides for removal of leakage water, measurement and control actions.
2. Description of the Prior Art
The problem with this type of equipment is how to utilize efficiently the variable speed of the water current for production of electrical energy on a constant voltage and frequency level, typically 50 or 60 Hz.
Usually, the problem is solved by using a turbine controller which ensures a constant rotational speed of the generator independently from the changing velocity of the water current and the actual electrical load. A turbine controller causes a significant complication and price increase.
Another method accepts that the generator's rotational speed, electrical frequency and voltage varies following the water current's velocity changes but through application of an electrical frequency and voltage converter transforms the generated variable frequency and voltage into a constant electrical frequency and voltage. The requirement on a constant voltage and frequency is based on the assumption that all energy will be transported and used as 50 or 60 Hz power.
The cost of a frequency and voltage converter is significant.